Electric furnace.



A. DOW.

ELEcRlc FURNACE.

APPLICATION FILED MAY 29, i914. 1,161,634. Patented Nov. 23, 1915.

Wl T/VESSES:

l INVENTOR @f/w24 ALEX DOW, 0F DETROIT, MICHIGAN.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Nov. 23, 1915.

Application filed May 29. 1914. Serial No. 841,740.

of Michigan, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification, reference being had therein to the accompanying drawings.

The invention relates to electric furnaces,-

and particularly to that class in which a resistor 1s formed by a body of granular materlal. such, as coke or other form of carbon.

A'ith such constructions it is usual to place the granular body within a casing or holder of refractory and electrically insulating material, the terminals being arranged at opposite ends of this casing and the heat being generated by the comparatively high resistance of the granular material. The work is arranged to receive the heat by radiation from the exposed surface of the resistor body, and the temperature may be regulated b v variation in the pressure upon said body.

A serious difficulty which has been experienced with furnaces of this type is that of controlling the path of the current through the resistor body. It is desirable to use a bed of some considerable thickness in order to obtain a more uniform resistance and to compensate for loss by surface oxidation. This, however, renders it difficult to maintain uniform electrical resistance through the cross section of the bed and `there is a constant tendency toward the lowering of the "resistance at the bottom of the bed and the increasing of the resistance at the work surface thereof. This is due partly to the fact that carbon has a negative temperature coefficient and the lowering of the temper-l ature of the exposed surface, due to radiation and absorption by the work will increase the resistance thereof. This will result in the deflection of the current into 'a lower portion of the resistor bed, with the objectionable effect of increasing the heat developed adjacent to the refractory lining, while diminishing the heat generation at the surface Where it is most effective for distribution to the work. Thus the efficiency of the apparatus is lessened and the intensified heat 1n the lower strata of the resistor has a detrimental effect upon the refractory case.

With the present invention I overcome this objection by the provision of meansfor deflecting the current into a path adjacent opposite ends of the casing.

to the work-distributing surface of the resistor.' Preferably electro-magnetic means is employed for this purpose, and where, as 1s usual, alternating current is employed the magnetism may be produced inductively thereby.

Various constructions may be employed for carrying out my invention, but, as shown,-Figure l is a longitudinal section through a furnace to which my improvement is applied; Fig. 2 is a cross section thereof; Fig. 3 is a plan view of the frame of magnetic bars; Fig. 4 is a cross. section showing the electrically insulated mechanical connection between the bars; and Fig. 5 is a diagram showing a modified construct1on.

A is a casing formed of refractory rhaterial, within which is arranged a bed B of the granular resistor material, with a work chamber C above the same having an openlng D for the insertion of the work therein. E are the terminals through which the current is supplied to the resistor arranged at With the construction as thus far described, when work, such as a metal bar E', is introducedinto the heating chamber it will be heated partly by direct radiation from the surface of the resistor bed and partly by reflection from the top of the chamber C. The rapid absorption of heat bythe work will, however, result in lowering the temperature of the surface ofthe bed, which will increase the electrical resistance thereof. and furthermore, where the work is a magnetic metal, such as iron, it will act inductively upon the current passing through the resistor, tending to deflect the same downward. This will have the objectionable results previously described. To utilize this effect, I have provided a series netic material` such as iron, which extend transversely of the path of current through the resistor and across the bottom of the casing A and also upward upon opposite sides thereof to approximately the level of the upper surface of the resistor bed. The bars F are supported in this position bya connection with longitudinally-extending bars G, but to avoid short circuiting, this connection is electrically insulated. Thus, as shown in Fig. 4, ythe bolt H which clamps each bar F to the bar G is provided with an insulating sleeve I and insulator washers J vand J to prevent electrical connection with of bars F Vof magsaid bars, while an insulating strip K inter posed between the bars prevents direct electrical connection therebetween.

iith the construction as described, when current is applied to the furnace it will pass principally through that portion of theresistor adjacent to the lworking surface 'of the resistor, thereby intensifying the heat at this point and diminishing the heating effect adjacent to the refractory7 lining. This action is due to the fact that the metallic bars described are arranged each with its respective magnetic axis so related to the ,line of fiow of electric current as to permit the induction of maximum magnetism and thereby cause the greatest repulsion of current.

Where desired, the effect may be still further intensified by forming onev or more convolutions of the conductor L around the cross section of the bars I*` before the current enters the resistor body, as shown in Fig. 5.

IVhat I claim as my invention is 1. In an electric furnace, the combination with a refractory casing, of a resistor bed therein having an exposed surface, terminals passing throughopposite walls of the casing through which current is supplied to the resistor bed, and electro-magnetic means for defiecting the path of the current through said bed toward the exposed surface v thereof.

2. In an electric furnace, the combination with a refractory casing having a work chamber, of a resistor bed within the casing adjacent to said chamber, and electro-magnetic means for defiecting the path of the current through said bed toward the work chamber.

3. In an electric furnace, the combination of a refractory casing and a resistor bed therein, of electro-magnetic means for deflecting the path. of the current through said resistor from the surface adjacent to` said casing toward the exposed surface thereof.

4; In an electric furnace, the combination with a resistor, of terminals engaging opposite points of the same through which current is supplied to the resistor, and a series of magnetic bars arranged trans-v versely of the path of the current througl'i said bed for deflecting the current toward a. certain surface of the resistor.

5. In an electric furnace, the combination with ay refractory case, of a resistor bed therein, and a series of magnetic bars arranged transversely of said bed across the bottom thereof for deflecting the current toward the upper surface.

6. In an electric furnace, the combination with a. refractory casing, of a resistor bed therein, and 'a serios of magnetic bars extending transversely across the bottom of said casing and upward along the sides thereof, for the purpose described.

7. In an electric furnace, the combination With aV refractory case and a resistor bed therein, of a frame comprising a. series of transversely-extending magnetic bars and longitudinally-extending bars connected to and insulated therefrom, said frame being arranged with the magnetic bars extending transverse to the path of the current through said resistor bed to defiect the same to the upper surface thereof.

8. In an electric furnace, the combination with a refractory case, of a resistor bed therein, and av frame formed of parallel-U- shaped magnetic bars and connecting cross bars insulated therefrom. said frame being arranged with said parallel bars extending transverse to the path of the current through said resistor and extending across -the bottom and upward along the sides of said case,

9. In an electric furnace, the combination with a resistor. of a metallic body arranged adjacent to said resistor, producing deflection of the current passing through the re- Esistor through the induction by the resistor of a magnetic field in said body.

10. In an electric furnace, the combination with a refractory casing and a resistor bed therein, having` an exposed work surface, of a metallic body exterior to the casing. producing a deflection of the current ALEX DOW.

signature Witnesses: v ED. L. CROSBY, FRANCES FLUsKEY.

Copies of this patent may be obtained for fii'vre cents each, by addressing the Commissioner of Patents,

Washington, D. C. 

